The handling of plastic bags downstream of a bag making machine is described in the following commonly owned U.S. Pat. Nos. 4,270,908 issued 2 June 1981; 4,333,298 issued 8 June 1982; 4,342,564 issued 3 Aug. 1982; 4,378,268 issued 29 Mar. 1983; 4,398,903 issued 16 Aug. 1983; 4,368,051 issued 11 Jan. 1983; 4,395,252 issued 26 Feb. 1983; 4,549,877 issued 29 Oct. 1985; 4,662,864 issued 5 May 1987; 4,536,174 issued 20 Aug. 1985; 4,552,551 issued 12 Dec. 1985; 4,512,757 issued 23 Apr. 1985; 4,614,472 issued 30 Sept. 1986; 4,695,346 issued 22 Sept. 1987 and 4,631,047 issued 23 Dec. 1986.
Reference may also be had to copending application Ser. No. 7/205,432 filed 10 June 1988.
From these patents and the copending application, it will be apparent that a star-type wheel may be used to transfer bags arriving from the outlet end of a plastic bag making machine to a stacking location at which the bags are stacked by threading them onto pins which can accommodate a number of such bags for further processing, e.g. joining of the bags of the stack onto a pad or collection.
The bags may be so stamped to form so-called "shirt" bags, and the star wheel arrangement can be provided with a variety of other elements to properly position and manipulate the bags.
In U.S. Pat. No. 4,451,249, for example, a bag handling apparatus is described which comprises a star wheel-type transfer device, a pin or needle stacker onto which the bags carried by the star wheel are threaded, and a stamping device.
The star wheel transfer device has suction arms which grip the bags as they arrive from an automatic plastic bag making machine and carry the bags onto the needles of the stacking device until a bag stack of a predetermined number of bags is found in the stacking position. In a periodic manner, the stack is moved from the stacking or needle-threading position. Of course, a transport device must be provided downstream of the stacker to allow this action.
In the prior art device of U.S. Pat. No. 4,451,249, the star wheel requires two plastic bags hanging together to be moved transversely. The pickup device moves intermittently in the working direction and has the form of a conveyor belt provided with the needles. The interconnected pair of plastic bags which are to be stacked by the star wheel are caused to be deposited above this conveyor in a saddlelike orientation, are threaded onto needles and are divided on this conveyor so that two stacks are formed thereon. The formation of two bag stacks by the movement carried out by the star wheels of two bags hanging together, provides a relatively high air resistance to movement of the bags.
This creates problems in practice, because the bags are held only by suction to the suction arms. To prevent an uncontrolled shifting of the bags carried by the arms, the movements cannot be too rapid and the cycling time of the apparatus must not be excessive. This means that the speed at which the bags are stacked cannot be high either.
This presents a serious problem because bag making machines are increasingly being designed to supply bags at faster speeds.